There is known an apparatus which reduces torque fluctuation of an internal combustion engine by making torque fluctuation which is antiphase with respect to torque fluctuation of an internal combustion engine by a generator motor (see Patent Literature 1). According to the apparatus of the Patent Literature 1, the connection and the shut off between a crankshaft and a sub-flywheel is controlled and phase matching is performed between the torque fluctuation of the internal combustion engine and the torque fluctuation of the generator motor, and thereby, it is possible to enhance the effect of reduction of the torque fluctuation. Further, as prior art documents relating to the present invention, there are Patent Literatures 2 and 3.